| Wheat is an important grain crop in China and is widely planted in the region.At present,wheat is mainly sown by external slotted wheel seeder,and the conventional external slotted wheel seeder has pulsation phenomenon when sowing seed,which has the problems of high seed consumption,insufficient stability of each row and easy to cause leakage,lack of seedlings,broken monopoly,etc.The thesis addresses the shortcomings of conventional external slotted wheel wheat seeder and combines the urgent demand for wheat precision centralized seeder in actual production,and designs a key component of air-assisted centralized metering device based on polygonal slot wheel centralized seed feed and horizontal airflow.The key components of air-assisted centralized metering device based on polygonal slot wheels for centralized seed feed and horizontal airflow are designed to improve seed mobility during seed filling and seed feed,and to achieve stable seed transport and uniform distribution in each row by conveying airflow in the horizontal feeding device.The main research contents and conclusions are as follows.(1)Based on the systematic analysis of the current situation of wheat cultivation at home and abroad,the research status of seed discharge technology and its devices,the overall design of theair-assistedwheat collecting and discharging system based on equalwidth polygonal slot wheels for seed stirring,seed filling and seed feed,and horizontal feeding device for seed mixing and delivery was designed based on the real demand of wheat precision collecting and discharging,and its working process and principle were explained,and theair-assistedcollecting and discharging device for seed feed and feeding device were developed.The structure of key components and their parameters were developed.(2)The design and analysis of the seed feed device of the air-assisted wheat centralized metering device for wheat were carried out.The theoretical analysis shows that the equal-width polygonal slot wheel can drive the seed population to move along the tangential direction of the slot wheel surface,increase the seed filling time and improve the seed filling probability;the analysis determines the ranges of the length,width and depth of the slot wheel are 7～11mm,4～8mm and 3～5mm respectively,and the inclination angle of the slot wheel is 30°～50°.The range is 30°～50°,and the number of individual slot wheel holes is 28.(3)Simulation experiments on the effect of the structure of seed feed device on seed filling performance and wheat seed flow analysis based on EDEM discrete element simulation were carried out,including.(1)The effects of different slot wheel shapes on seed disturbance and seed filling performance were analyzed by EDEM simulation.The simulation test results showed that:the seed disturbance capacity in descending order was equal-width trilateral slot wheel,equal-width pentagonal slot wheel,equal-width heptagonal slot wheel,and circular slot wheel,and the average kinetic energy of the seeds of equal-width trilateral,equal-width pentagonal,and equal-width heptagonal slot wheels were increased by The average kinetic energy of equal-width trigonal,equal-width pentagonal,and equal-width heptagonal slot wheels increased by 371.3%,209.2%,and 91%,respectively,compared with that of circular slot wheels.(2)The influence of the seed feed device speed on the seed disturbance performance was analyzed by EDEM simulation,and it was determined that the seed disturbance capacity of the equal-width trilateral,equal-width pentagonal and equal-width heptagonal slot wheels was positively correlated with the speed of the seed feed device;when the speed range was 10～50r/min,increasing the speed of the seed feed device could improve the seed disturbance capacity of the slot wheel.(3)Analysis was conducted to determine the effects of structural parameters and installation position of the seed layer adjustment plate on the seed filling performance.Simulation analysis showed that the seed layer adjustment plate is suitable for stable seed filling when the transverse size of the plate is 45 mm,the longitudinal size is 20 mm,the bottom inclination angle of the plate is 20°,and the seed filling angle is close to 60°.(4)The parabolic hole structure was improved by using the secondary rotation orthogonal combination test,and it was determined that the average number of seed filling grains was 2 and the leakage rate was 2.22% when the depth of the hole was 4.68 mm,the inclination angle of the hole was 39.32° and the length of the hole was 9.26 mm,and the seed filling performance was better.(4)Based on CFD-DEM gas-solid coupling simulation,the influence of the structural parameters of the feeding device on the seed mixing and seed delivery process was analyzed to reveal the influence law of the horizontal conveying feeding device on the seed discharge performance of wheat,and the better structural type of the feeding device was determined,specifically including.(1)The results of Fluent simulation tests on the structural parameters of the feeding device show that: the contraction section is the main link where the pressure loss occurs,in order to make the seeds accelerate through the mixing chamber as soon as possible,the 40°cone angle of the contraction section with higher airflow speed inside the mixing chamber and relatively smaller airflow pressure loss is selected;the length of the mixing chamber has less influence on the extreme value of airflow speed and pressure loss,and the high-speed area generated when the length of the feeding device is 25 mm The smaller the cone angle of the expansion section,the smoother the transition of the pressure gradient in the expansion section,which is conducive to the smooth acceleration of the seeds in the expansion section and avoid collision with the tube wall and other seeds;based on the pressure gradient changes and the law of seed collision,the cone angle of the expansion section is determined to be 20°.The CFD-DEM coupling simulation results of different structure feeding devices show that the probability of collision between seeds leaving the mixing chamber and the inner wall of the pipe is higher in Type 1 and Type 2 feeding devices than in Type 3 and Type 4 feeding devices,and Type 1 and Type 2 feeding devices are more likely to cause disorderly movement of seeds in the feeding device and affect the movement of seeds in the feeding area,which is not conducive to stable and continuous seed feeding.The type 3feeding device has better seed discharge performance,and the seeds mainly move along the middle and lower part of the pipe with stable and continuous movement traces.(5)The experimental study on the performance of air-assisted centralized metering device was carried out,and the effect of the rotational speed of the seed feeding device on the mean value of total discharge,the coefficient of variation of total discharge stability,the mean value of each row of discharge,the coefficient of variation of each row of discharge consistency and the breakage rate was obtained through single-factor test: the mean value of total discharge and the mean value of each row of discharge were linearly correlated with the rotational speed,the coefficient of variation of total discharge stability,the coefficient of variation of each row of discharge consistency The coefficient of variation of the total displacement stability and the coefficient of variation of the consistency of each row of displacement are lower than 3.7%,and the breakage rate is lower than 0.4%,which meets the design requirements of the centralized seeder. |
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